1. Field of Invention
This invention relates to an electric drive control apparatus, an electric drive control method and a program therefor.
2. Description of Related Art
In a conventional electric drive unit that is mounted on a vehicle, for example, an electric vehicle or electric car, drive motor torque from a drive motor is transmitted to drive wheels in order to obtain a driving force. Further, in an electric drive unit that is mounted on an electric vehicle or a hybrid vehicle that transmits part of the engine torque to a generator (generator-motor), which is a first electrically operated machine, and that transmits the rest of the engine torque to the drive wheels, a planetary gear unit is provided. The planetary gear unit includes a sun gear, a ring gear and a carrier, to couple the carrier to the engine, to couple the ring gear to the drive wheels, to couple the sun gear to the generator, and to transmit the rotation produced by the ring gear and by a drive motor, which is a second electrically operated machine, to the drive wheels to obtain a driving force.
In the generator and the drive motor, a rotor is arranged such that the rotor is allowed to freely rotate. The rotor also has a pair of magnetic poles comprising permanent magnets of a N-pole and a S-pole. The drive motor also includes a stator disposed on the outer side of the rotor in the radial direction and having stator coils of U-phase, V-phase and W-phase.
The electric car is furnished with a drive motor control apparatus as an electromechanical controller. The hybrid vehicle is furnished with a generator control apparatus and a drive motor control apparatus as an electrically operated machine control apparatus. Pulse width modulation signals of the U-phase, V-phase and W-phase generated by the electrically operated machine control apparatus are sent to an inverter, and phase currents generated by the inverter are fed. In other words, currents of the U-phase, V-phase and W-phase are fed to the stator coils to energize the drive motor to thereby obtain a drive motor torque, or to drive the generator to obtain a generator torque.
In the above drive motor control apparatus, for example, a feedback control is executed by a vector control operation on a d-q axis model by setting a d-axis in a direction of the magnetic pole pair of the rotor, and setting a q-axis in a direction at right angles with the d-axis. In the drive motor control apparatus, therefore, currents fed to the stator coils are detected as detection currents, are converted into a d-axis current and a q-axis current, and the feedback control is executed based on the d-axis current, the q-axis current, a d-axis current instruction value and a q-axis current instruction value representing a target value. (see, for example, JP-A-11-332298).
When, for example, a driver attempts to quickly start the electric car by depressing the accelerator pedal, the d-axis current instruction value and the q-axis current instruction value may often change sharply. However, when the sampling period of the detection current is long, the gain in carrying out the feedback control cannot be increased. Therefore, the sampling periods are substantially shortened by estimating a d-axis current and a q-axis current after one sampling time, and by executing the proportional integration control based on the estimated d-axis current, q-axis current and on the d-axis current instruction value and q-axis current instruction value.
FIG. 2 is a block diagram illustrating a major portion of a conventional electric drive unit. In FIG. 2, reference numeral 31 denotes a drive motor (M) and 40 denotes an inverter that generates currents Iu, Iv and Iw of U-phase, V-phase and W-phase and feeds them to the drive motor 31. Reference numeral 45 denotes a drive motor control apparatus which includes a three phase/two phase converter unit 61, subtractors 62, 63, voltage instruction value generator units 64, 65, and a two phase/three phase converter unit 67. A drive circuit that is not shown is provided outside the drive motor control unit 45, and a PWM generator that is not shown is provided in the drive motor control unit 45.
The drive motor 31 is allowed to freely rotate, and includes a rotor (not shown) having a pair of electrodes comprising permanent magnets of N-pole and S-pole, and a stator (not shown) arranged outside of the rotor in the radial direction and having stator coils of U-phase, V-phase and W-phase. There are further arranged current sensors 33 and 34 for detecting the currents fed to the U-phase and V-phase stator coils, and a magnetic pole position sensor (not shown) for detecting the magnetic pole position θ of the rotor.
A torque instruction/current instruction converter unit (not shown) in the drive motor control unit 45 reads a battery voltage detected by a battery voltage sensor (not shown), i.e., reads the rotational speed NM of the drive motor 31 calculated based on the battery voltage VB and the magnetic pole position θ, reads a target torque TM* of the drive motor from the vehicle control apparatus that controls the vehicle as a whole, makes reference to a map of current instruction values (not shown), calculates a d-axis current instruction value id* and a q-axis current instruction value iq*, and sends them to subtractors 62 and 63.
Here, to conduct the feedback control operation, the drive motor control unit 45 reads detection currents iu and iv from the current sensors 33 and 34, and reads the magnetic pole position θ from the magnetic pole position sensor. The three phase/two phase converter unit 61 effects the three phase/two phase conversion based on the detection currents iu, iv and the magnetic pole position θ, and converts the detection currents iu, iv into a d-axis current id and a q-axis current iq.
Next, the d-axis current id is sent to a current estimation unit 71 which calculates and estimates a d-axis current after one sampling timing, and the estimated d-axis current idp is sent to the subtractor 62. The subractor 62 calculates a d-axis current deviation Δid between the d-axis current idp and the d-axis current instruction value id*. The d-axis current deviation Δid is sent to the voltage instruction value generator unit 64.
The voltage instruction value generator unit 64 includes a proportional integration operation unit (PI) 73 and a subtractor 74. The proportional integration operation unit 73 calculates a voltage drop Vzd based on the d-axis current deviation Δid, a gain Kp for the proportional operation and a gain Ki for the integration operation. The subtractor 74 subtracts an induced voltage ed due to the q-axis current iq from the voltage drop Vzd, generates such a d-axis voltage instruction value vd* so that the d-axis current deviation Δid becomes zero (0), and sends the d-axis voltage instruction value vd* to the two phase/three phase converter unit 67.
On the other hand, the q-axis current iq is sent to a current estimation unit 72 which estimates a q-axis current iqp after one sampling timing, and the estimated q-axis current iqp is sent to the subtractor 63. The subractor 63 calculates a q-axis current deviation Δiq between the q-axis current iqp and the q-axis current instruction value iq*. The q-axis current deviation Δiq is sent to the voltage instruction value generator unit 65.
The voltage instruction value generator unit 65 includes a proportional integration operation unit (PI) 75 and an adder 76. The proportional integration operation unit 75 calculates a voltage drop Vzq based on the q-axis current deviation Δiq. The adder 76 adds an induced voltage eq due to the d-axis current id to the voltage drop Vzq, generates such a q-axis voltage instruction value vq* so that the q-axis current deviation Δiq becomes zero (0), and sends the q-axis voltage instruction value vq* to the two phase/three phase converter unit 67.
Then, the two phase/three phase converter unit 67 effects the two phase/three phase conversion, reads the d-axis voltage instruction value vd*, q-axis voltage instruction value vq* and magnetic pole position θ, converts the d-axis voltage instruction value vd* and q-axis voltage instruction value vq* into voltage instruction values Vu*, Vv* and Vw* of U-phase, V-phase and W-phase, and sends the voltage instruction values Vu*, Vv* and Vw* to the PWM generator.
Based on the voltage instruction values Vu*, Vv* and Vw* of the above phases and on the battery voltage VB, the PWM generator generates pulse width modulation signals Mu Mv and Mw of the above phases having pulse widths corresponding to the d-axis current instruction value id* and the q-axis current instruction value iq*, and sends them to the drive circuit.
Upon receipt of the pulse width modulation signals Mu, Mv and Mw of the phases, the drive circuit generates six gate signals and sends them to the inverter 40. The inverter 40 includes transistors Tr1 to Tr6 that are not shown, renders the transistors Tr1 to Tr6 conductive only during the period in which the gate signal is on to generate currents Iu, Iv and Iw of the above phases, and feeds the currents Iu, Iv and Iw of the above phases to the stator coils of the drive motor 31.
The torque is thus controlled based on the target torque TM* of the drive motor, whereby the drive motor 31 is driven and the electric car travels. Thus, the feedback control is executed based on the d-axis current instruction value id*, q-axis current instruction value iq* and the estimated d-axis current idp and q-axis current iqp. Therefore, even when the actual sampling periods for the detection currents iu and iv are long, the sampling periods can be substantially shortened. In conducting the feedback control, therefore, the gains Kp and Ki can be increased, enabling the d-axis current id and the q-axis current iq to follow the d-axis current instruction value id* and the q-axis current instruction value iq*, and the transient characteristics can be maintained.
Here, a real current is constituted by the d-axis current id and the q-axis current iq, a current instruction value is constituted by the d-axis current instruction value id* and q-axis current instruction value iq*, and an estimated current is constituted by an estimated d-axis current idp and an estimated q-axis current iqp.